Known in the art is a so-called “through-spindle coolant supply system” which is comprised of a coolant channel running axially through a spindle of a machining center or other machine tool and a tool holder and tool attached to the same and discharges coolant from the tip of the tool. PTL 1 describes a tool holder used in such a through-spindle coolant supply system. The tool holder receives coolant from a coolant supply pipe at the spindle side, so a coolant pipe extending to the spindle side is necessary. The coolant pipe is a part which is discarded along with a tool changing operation. For this and other reasons, usually, as shown in PTL 1, one which is fabricated as a separate member from the tool holder is screwed into the tool holder.